Calutrons



Dec. 13, 1955 E. o. LAWRENCE CALUTRONS 3 Sheets-Sheet 1 Filed Sept. 2, 1944 ACCELERAI/A/G ELECTRODE SUPPLY ARC SUPPLY F/LAMENT SUPPLY HEA TE SUPPLY m up Na 0 AF M Fig. 2

INVENTOR. ERA/57 0. AA WRENCE ATTORNEY.

Dec. 13, 1955 o. LAWRENCE CALUTRONS 3 Sheets-Sheet 2 Filed Sept. 2, 1944 INVENTOR. E R/VES r 0. LA WRE/VC'E ATTORNEY.

United States Patent CALUTRONS Ernest 0. Lawrence, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application September 2, 1944, Serial No. 552,544

6 Claims. (Cl. 250-413) The present invention relates to electric discharge devices and more particularly to calutrons.

it is an object of the invention to provide a calutron transmitter of the type wherein the ion source is at a high positive potential with respect to the calutron tank, which calutron transmitter may be operated at higher potentials than has been heretofore feasible.

Another object of the invention is to provide a calutron transmitter of the type wherein the ion source is at a high positive potential with respect to the calutron tank in which the high voltage current drain is minimized.

A further object of the invention is to provide in an electric device including electrodes that are at high poten tials with respect to the surrounding region and that are positioned in a magnetic field, an arrangement for minimizing current drains to the electrodes and for reducing er and erosion of the electrodes.

The invention, both as to its organization and method of operation, together with other objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which Figure l is a diagrammatic plan view of a calutron into which there may be incorporated a transmitter embodying the present invention; Fig. 2 is a mirror image view taken along the section line 22 in Fig. 1; Fig. 3 is a diagrammatic plan view of a calutron transmitter embodying the present invention; Fig. 4 is a side elevational view, partially in section, of a calutron transmitter embodying the present invention; 5 is a sectional view of the calutron transmitter taken along the line 5-5 in Fig. 4; and Fig. 6 is a sectional view of the shielding arrangement of the calutron transmitter taken along the line 66 in Fig. 5.

At the outset, it is noted that a calutron is a machine of the character of that disclosed in the copending application of Ernest 0. Lawrence, Serial No. 557.784, filed October 9, 1944, now Pat. No. 2,709,222, and is employed to separate the constituent isotopes of an element and, more particularly, to increase the proportion of a selected isotope in an element containing several isotopes in order to produce the element enriched with the selected isotope. For example, the machine is especially useful in producing uranium enriched with U Such a calutron essentially comprises means for vaporizing a quantity of material containing an element that is to be enriched with a selected one of its several isotopes; means for subjecting the vapor to ionization, whereby at least a portion of the vapor is ionized, causing ions of the several istopes of the element to be produced; electrical means for se regating the ions from the un-ionized vapor and for accelerating the segregated ions to relatively high velocities; electromagnetic means for deflecting the ions along curved paths, the radii of curvature of the paths of the ions being proportional to the square roots of the masses of the ions, whereby the ions are concentrated in accordance with their masses; and means for tie-ionizing and collecting the ions of the selected isotope thus concentrated, thereby to produce a deposit of the element enriched with the selected isotope.

2,727,150 Patented Dec. 13, 1955 Referring now more particularly to Figs. 1 and 2 of the drawings, there is illustrated a representative example of a calutron 10 of the character noted, that comprises magnetic field structure including upper and lower pole pieces 11 and 12, provided with substantially fiat parallel spaced apart pole faces, and a tank 13 disposed between the pole faces of the pole pieces 11 and 12. The pole pieces and 12 carry windings, not shown, which are adapted to be energized in order to produce a substantially uniform and relatively strong magnetic field therebetween, which magnetic field passes through the tank 13 and the various parts housed therein. The tank 13 is of tubular configuration, being substantially crescent-shaped in plan, and comprising substantially fiat parallel spacedapart top and bottom walls 14 and 1:5, upstanding curved inner and outer side walls 16 and 17, and end walls 18 and 19. The end walls 18 and 19 close the opposite ends of the tubular tank 13 and are adapted to be removably secured in place, whereby the tank 13 is hermetically sealed. Also, vacuum pumping apparatus, not shown, is associated with the tank 15, whereby the interior of the tank 13 may be evacuated to a pressure of the order of 1O to 10 mm. Hg. Preferably, the component parts of the tank 13 are formed of steel, the top and bottom walls 14- and 15 thereof being spaced a short distance from the pole faces of the upper and lower pole pieces 11 and 12, respectively, the tank 13 being retained in such position in any suitable manner, whereby the top and bottom walls 14 and 15 constitute in efiect pole pieces with respect to the interior of the tank 13, as explained more fully hereinafter.

The removable end wall 18 suitably supports a source unit 29 comprising a charge receptacle 21 and a communicating arc-block 22. An electric heater 23 is arranged in heat exchange relation with the charge receptacle 21 and is adapted to be connected to a suitable source of heat supply, whereby the charge receptacle 21 may be appropriately heated, the charge receptacle 21 being formed of steel or the like. The arc-block 22 is formed, at least partially, of carbon or graphite and is substantially C-shaped in plan, an upstanding slot 24 being formed in the wall thereof remote from the charge receptacle 21. Thus, the arc-block 22 is of hollow construction, the cavity therein communicating with the interior of the charge receptacle 21.

Also, the removable end wall 18 carries a filamentary cathode 25 adapted to be connected to a suitable source of filament supply, the filamentary cathode 25 overhanging the upper end of the arc-block 22 and arranged in alignment with respect to the upper end of the cavity formed therein. The arc-block 22 carries an anode 26 disposed adjacent the lower end thereof and arranged in alignment with respect to the cavity formed therein. Also, the arc-block 22 carries a collimating electrode 2? disposed adjacent the upper end thereof and having an elongated collimating slot 28 formed therethrough and arranged in alignment with respect to the filamentary cathode 25 as well as the anode 2 6 and the cavity formed in the arc-block 22. Both the anode 26 and the collimating electrode 27 are electrically connected to the source unit 21) which, in turn, is insulated from the tank 13, the tank 13 being grounded. Also, the filamentary cathode 25 and the cooperating anode 26 are adapted to be connected to a suitable source of arc supply.

Further, the removable end wall carries ion accelerating structure 39 formed of carbon or graphite and disposed in spaced-apart relation with respect to the wall of the arc-block 22 in which the slot 24 is formed. More specifically, a slit 40 formed in the ion accelerating structure 39 and arranged in substantial alignment with respect to the slot 24 formed in the wall of the arc-block 22. A suitable source of accelerating electrode supply is adapted to be connected between the arc-block 22 and the ion accelerating structure 39, the positive and negative terminals of the supply mentioned being respectively connected to the arc-block 22 and to the ion accelerating structure 39. Further, the ion accelerating structure39 is connected to the tank 13, which may be considered as at ground potential.

The removable end wall 19 suitably supports a collector block 29 formed of stainless steel or the like and provided with two laterally spaced-apart cavities or pockets 30 and 31 which respectively communicate with aligned slots 32 and 33 formed in the wall of the collector block 29 disposed remote from the removable end wall 19. The pockets 39 and 31 are adapted to receive two constituent isotopes of an element which have been separated in the calutron 10, as explained more fully hereinafter. Itwillbe understood that the tank 13 constitutes an electrostatic shield for the high velocity ions traversing the curved paths between the slit 40 formed in the ion accelerating structure 39 and the slots 32 and 33 formed in the collector block 29, as explained more fully hereinafter. It is noted that the accelerating structure 39, the tank 13, and the collector block 29 are connected to the negative grounded terminal of the accelerating electrode supply; while the ion source 20 is connected to the ungrounded positive terminal of the accelerating electrode supply and is electrically insulated from the component parts of the tank 13.

Considering now the general principle of operation of the calutron 10, a charge comprising a compound of the element to be treated is placed in the charge receptacle 21, the compound of the element mentioned being one which may be readily vaporized. The end walls 18 and 19 are securely attached to the open ends of the tank 13, whereby the tank 13 is hermetically sealed. The various electrical connections are completed and operation of the vacuum pumping apparatus, not shown, associated withthe tank 13 is initiated. When a pressure of the order of 10- to min. Hg is established within the tank 13, the electric circuits for the windings, not shown, associated with the pole pieces, 11 and 12 are closed and adjusted, whereby a predetermined magnetic field is established therebetween traversing the tank 13. The electric circuit for the heater 23 is closed, whereby the charge in the charge receptacle 21 is heated and vaporized. The vapor fills the charge receptacle 21 and is conducted into the communicating cavity formed in the arc-block 22. The electric circuit for the filamentary cathode, 25 is closed, whereby the filamentary cathode is heated and rendered electron emissive. Then the electric circuit between the filamentary cathode 25 and the anode 26 is closed, whereby an arc discharge is struck therebetween, electrons proceeding from the filamentary cathode 25 through the collimating slot 28 formed in the collimating electrode 27 to the anode 26. The collimating slot 28 formed in the collimating electrode 27 defines the cross section of the stream of electrons proceeding into thearcblock 22, whereby the arc discharge has a ribbon-like configuration and breaks up the molecular form of the compound of the vapor to a considerable extent, producing positive ions of the element that is to be enriched with the selected one of its isotopes.

The electric circuit between the arc-block 22 and the ion accelerating structure 39 is completed, the arc-block 22 being at a high positive potential with respect to the ion accelerating structure 39, whereby the positive ions in the arc-block 22 are attracted by the ion accelerating structure 39 and accelerated through the voltage irnpressed therebetween. More particularly, the positive ions proceed from the cavity formed in the arc-block 22 through the slot 24 formed in the wall thereof, and across the space between the ion accelerating structure 39 and the adjacent wall of the arc-block 22, and thence through the slit 40 formed in the ion accelerating structure 39 into the substantially electric-fieldrfree space defined by uranium.

the walls of the tank 13 beyond the accelerating structure 39'. The high-velocity positive ions form a vertical upstanding ribbon or beam proceeding from the cavity formed in the arc-block 22 through the slot 24 and the aligned slit 40 and through the interior of the tank 13.

As previously noted, the collector block 29, as well as the tank 13, is electrically connected to the ion accelerating structure 39, whereby:- there is an electric-field-free path for the high-velocity positive ions disposed between the ion accelerating structure: 39and the collector block 29 within the tank 13 The high velocity positive ions leaving the slit 40 formed in the accelerating structure 39 are deflected from their normallstraightsline pathand from a vertical plane passing through the slot 24 and the aligned slit 40, due to the efiec't' ofth'e relatively'strong magnetic field maintained through the space within the tank 13 through which the positive ions travel, whereby the positive ions describe arcs, the radiiof which are proportional to the square roots of the masses of the ions and consequently of the isotopes. of the element mentioned. Thus, relatively light ions,'av relatively light isotope of the element, describe an interior arc of relatively short radius and are focused through the slot. 32 into the pocket formed in the collector block 29; whereas relatively heavy ions, a relatively heavy isotope ofthe element, describe an exterior arc of relatively long radius and are focused through the slot 33 intothe pocket 31 formed in the collector block 29. Accordingly, the relatively light ions are collected in the pocket 30 and, are deionized to produce a deposit of the relatively light isotope of the element therein; while the relatively heavy ions are collected in the pocket 31 and are de-ionized to produce a deposit of the relatively heavy isotope of the element therein.

After all of the charge in the charge receptacle 21 has been vaporized, all of-the electric circuits are interrupted and the end wall'18 is'removed so-that another charge may be placed in the charge receptacle 21 and subsequently vaporized in the manner explained above. After a suitable number of charges have been vaporized in order to obtain appropriate depositsof theisotopes of the element in the pockets 30 and 31 of the collector block 29, the end, wall 19 may be removed and the deposits of the collected isotopes in the pockets30 and 31: in the collector block 29 may bereclaimed;

Of course, it will be understood; that the various dimensions of the parts of the calutron 10, the various electrical potentials applied between the various electrical parts thereof, as well. as the strength ofthe. magnetic field between the pole pieces 11 and 12, are suitably correlated with respect to each other, depending upon the mass numbers of the several isotopes of the element which is to be treated therein. In this connection, reference is again made to the copending application of Ernest 0. Lawrence, for a complete specification. of a calutron especially designed for theproduction of uranium enriched with the isotope U By way of illustration, it is noted that when the calutron 10 is employed in order to produce uranium enriched. with U 3 the compound of uranium that is suggested as a suitablecharge in the charge receptacle 21 is UCl4, as this compound may be readily vaporized and the molecular form of the vapor may be readily broken up to form positiveions of uranium with great facility. In this case, uranium enriched with U is collected in the pocket 30 of the collector block 29, and uranium comprising principally U 3 is collected in the pocket 31 of the-collector. block 29. Also, it is noted that from a practical standpoint, thedeposit of uranium collected in the pocket 30 0f the collector block 29 contains considerable amounts of U inview of the fact that this isotope comprises the dominant constituent of normal Furthermore, thedpositof uranium collected in the pocket 30 of the collector block- 29-contains a considerably increased amount of U in view of the fact that it is not ordinarily feasible to separate U and U in the production of relatively large quantities of uranium enriched with U for commercial purposes. Accordingly, in this example the uranium deposited in the pocket 30 of the collector block 29 is considerably enriched, both with U and with U and considerably impoverished with respect to U as compared to natural or normal uranium.

In the operation of the calutron 10, it is highly desirable that a relatively intense stable beam of positive ions be projected by the ion accelerating structure 39, through the tank 13, toward the collector block 29; which operating condition requires that the source unit 2!) be productive of a steady and copious supply of positive ions. To accomplish this end in the source unit 20, the arc discharge through the cavity in the arc-block 22 between the filamentary cathode 25 and the anode 26 must be both relatively intense and unfiorm. Moreover, it is desirable that such an arc discharge should be steady and free from both intensity and position variations in order that the ion source unit 20 be productive of a highly continuous, copious and uniform supply of positive ions. Furthermore, the ion source unit 20 should be so constructed and arranged that the parts thereof are subjected to minimum wear and erosion, whereby the unit has a long life and an efiicient operating characteristic.

While the source unit in the calutron disclosed in the previously mentioned copending application of Ernest 0. Lawrence, more specifically the source unit which is at a high positive potential with respect to the tank, is satisfactory, operation thereof is accompanied by a current drain which is large as compared to the energy imparted to the ion beam, thus resulting in a low electrical efficiency. Further, this large current drain limits the potential which can be applied to the accelerating structure, thereby further decreasing the over-all efficiency of the apparatus. Another defect which is present in the earlier ion source unit that is maintained at a high positive potential with respect to the tank is the frequent failures of insulators associated with the ion source unit, more particularly, the insulator which supports the ion source with respect to the tank and through which electrical leads which are at a high positive potential are led.

The aforementioned defects are attributable to electron oscillation occurring in the region immediately surrounding the ion source unit which is at a high positive potential. Electrons which originate in the region surrounding the source unit and Whose projections along the magnetic field associated with the calutron are uninterrupted by the source unit, have acting on them an electric field impelling them toward the source unit. This electric field may be resolved into a component parallel to the magnetic field and a component normal to the magnetic field. inasmuch as the electrons are free to move in paths along the magnetic field, the electric field component which is parallel to the magnetic field will cause the electrons to traverse paths starting at the points of origin of the electrons in a direction along the magnetic field and toward a higher potential, and when such electrons reach points of maximum potential along their path the kinetic energy imparted thereto will cause the electrons to pass beyond these points and come to rest at points which are at the same potential as their point of origin. This process is successively repeated, thus resulting in an electron oscillation along the magnetic field. Superimposed upon this oscillatory electron motion there is a cycloidal motion of small radius imparted to the electrons by the electric field component normal to the magnetic field. Moreover, the electrons which have the motions set forth above also possess an over-all drift normal to the electric and magnetic field and eventually terminate on any obstruction which might occur in their path, such as the source unit or its supporting insulator. It should be noted that the obstruction must necessarily be at a positive potential relative to the potential at the rest point of the oscillating electron. However, before the motion of the electron is thus terminated it may traverse a long path in the gaseous region surrounding the source unit, and in so doing may ionize molecules of the gas in such region, producing both electrons and positive ions. The electrons so produced in turn have motions imparted thereto similar to the original electrons and the result is, in general, an ionized region in the vicinity of the ion source, and consequential thereto, excessive current drains and insulator failures. These defects have been substantially remedied by reducing the number of oscillating electrons which are produced in the region of the ion source at a high positive potential. This has been accomplished by minimizing the volume of the electric field in which electron oscillation may occur and which surrounds the ion source, thereby reducing the total path traversed by the oscillating electrons and thus decreasing the over-all ionization of the gaseous region immediately surrounding the ion source. It should be noted that the volume in which electron oscillation may occur comprises the region of electric field surrounding the ion source whose projection along the magnetic field is unintercepted by the ion source or a conductor at substantially the same potential as the ion source.

Referring now more particularly to Figure 3 of the drawing, a calutron transmitter embodying the principles of the present invention is illustrated schematically in plan view. More particularly, a calutron tank 50 is provided with an end wall 51 having a rectangular opening 52 formed therethrough. Removably associated with the opening 52 is a face plate 53 Which is adapted to be positioned on the end wall 51, whereby the opening 52 is hermetically sealed. Further, the face plate 53 has formed therein a circular aperture 54, and extending from the face plate 53 is a cylindrical insulating bushing 56, the bushing 56 being coam'al with the cylindrical opening 54 A second face plate 57 is positioned on the free end of the insulating bushing 56. It should be noted that the face plate 53, insulating bushing 56 and second face plate 57, together with the calutron tank 50, form a substantially fluid-tight envelope.

Projecting from the face plate 57 is an ion source support 58 which has mounted at its end a yoke 59, the yoke 59 pivotally engaging the ion source unit 60. Electrically associated with the ion source 60 is an accelerating structure 1 comprising a pair of arms 63 projecting from the face plate 53 and supporting the accelerating electrode 64. Further, the shielding arrangement for suppressing electron oscillation consists of the inner shields as and 67' extending from the face plate 57, which shields are of substantially cylindrical configuration and surround the ion source unit 60 and the associated supporting structure 58 and 59. An outer electrical shield 68, also of cylindrical configuration, surrounds the inner shield 67 and is coaxial therewith, the shield 68 extending from the face plate 53. Moreover, the forward end of the ion source so has positioned thereon a vertical disk-shaped shield 69, and the electrode structure 61 supports a second disk-shaped shield 70, the shield being parallel to and adjacent the shield 69. It should be noted that the inner shields 66, 67 and 69, as well as the ion source unit 6t) and the supporting structure 58 and 59, are electrically connected to the face plate 7, which in turn is connected to a relatively high positive accelerating potential. Further, the outer cylindrical shield 63, the accelerating electrode support 63 and the accelerating electrode 64 are electrically connected to the face plate 53, which in turn is connected to the calutron tank 5 19 which is at ground potential. The shields 67 and 69 are sufiiciently spaced from the shields 68 and '78 so that there will be no electrical breakdown between them at the pressures at which a calutron is normally operated.

The arrangement described reduces the volume wherein electron oscillation might normally occur; that is, the region of electric field surrounding the ion source unit 60 and the associated structure 58 and 59 and extending to the side walls of the calutron tank 50 is greatly reduced. More particularly, the volume of the region of ion oscillation is now limited to the space defined by the inner surface of the outer shield 68 and vertical planes tangent to the outer surface of the inner shields 66 and 67. Thus, any electrons originating between the shields 67 and 68 are limited in their vertical motion by the aforesaid boundaries, thereby resulting in shortened paths, less oscillating electrons, and greatly reduced ionization in such region. Further, free electrons originating in the region above defined will drift in a clockwise direction; that is, such oscillating electrons will drift in a forward direction on the left side of the transmitter and will drift in a rearward direction on the right side of the transmitter, so

that the majority of the drifting electrons will terminate .on the right side of the insulator bushing 56. Employing 81 formed therein, and has removably positioned thereon a first metal face plate 82 which is in fluid-tight relationship with the end wall 80. Further, a circular opening '83 is formed in the face plate 82, which face plate 82 has mounted'thereon a cylindrical bushing 84 of glass, porcelain or other suitable insulating material, the bushing 84 being coaxial with the circular opening 83 and being hermetically secured to the face plate 82 by means of a pair of annular rings 35 and cooperating gaskets 86, of rubber or the like. Similarly positioned on the free end of the bushing 84 by means of the annular rings 87 and gaskets 88 is a second metallic face plate 89. Projecting inwardly from the central portion of the inner face of the face plate 89 is the tubular standard 90, which is mounted on the face plate by means of a series of bolts 91 passing through the flange 92 and securing the standard 9.0 to the face plate 89. A yoke member 94, positioned at theforward end of the standard 90, has a pair of projecting arms 95 which pivotally support an ion source 100. Rigidly mounted on the standard 90, anterior to the yoke-member 94, is a collar 96 having a pair of spaced verticalprojections 97 which engage a pair of adjusting screws '98. Extending rearwardly from the yoke member 94 into the groove between the projections 97 is the arm 99. Thus,.with the arrangement described, the angle of the yoke .member 94 and the supported ion source 100 maybe adjusted about the axis of the horizontal standard '90 by means of the adjusting screws 98.

The ion source 100 which is pivotally mounted between the arms 95 of the yoke member 94 comprises a charge reservoir 101, a diffusion chamber 102 and an arc chamber 103. Heating elements 105 are provided, whereby a charge contained within the charge reservoir 101 may be vaporized; and heating elements 105 are disposed in the side walls surrounding the diffusion chamber 102, whereby the vapor produced in the charge reservoir 101 is prevented from condensing on the Walls of the diffusion chamber 102. Further, the charge reservoir 101 communicates with the diffusion chamber 102 by means of a conduit 107, whereby vapor produced in the charge reservoir 101- passes into the diffusion chamber 107 and thence through ,a slit 108 formed in the forward wall of the diffusion chamber 102 into the arc chamber 103, wherein an electric arc is established, thus ionizing the vapor in the arc chamber 103. An electrode 109 is positioned on the front wall of the ion source 100 and has a vertical slit 110 formed therein through which the ioriized particles produced in the arc chamber 103 may be withdrawn. In order that the ion source may be adjusted 90,:an arm.111,ihaving its forward end. pivoted to--the l er- 0 tbci n sour e e end ri a wa and a threaded rod 112 engages a' tapped hole formed in the rear end of the arm 111, the rod 112 extending through 21 Wilson .seal 113 positioned in the face plate 89. Thus, the angular position of the ion source may be varied by means ofthe rod 112, a fine adjustment being obtained vby rotating the rod 112 and a coarse adjustment being obtained by moving the rod 112 inwardly or outwardly through the Wilson seal 113. Moreover, a spring 114 mounted on the yoke member 94 pushes against the arm 111, urging it in the forward direction.

The face plate 89 has formed therein a circular opening 120, and has mounted on its outer face by means of the collar 122 the cylindrical insulating bushing 121, which'is coaxial with the circular opening 120. Extending from the insulating bushing 121 is a vacuum-tight casing 122 which houses a universally mounted cathode support, ,whereby the cathode may be rotatably adjusted about apoint within the casing 122. Further, extending from the casing 122 is a vacuum lock arrangement, including the valve 123 and an arrangement 124 cooperating with a housing125' of the vacuum lock for adjusting the position of the cathode in a longitudinal direction. A cathode lead casing 125 coaxial with the casing 122 is removably and adjustably positioned, extending from the longitudinal adjusting arrangement 124 to a point above the arc chamber 103 and supporting a filament 126 at the forward end of the cathode lead casing 125.

Considering now the shielding arrangement for suppressing electron oscillation around the ion source, there is provided a pair of inner cylindrical shields 130 and 131, which are coaxial with the horizontal standard 90. The shield 130 is resiliently mounted on the face plate 89 by means of a pluralityv of nuts and studs 132, which studs pass through an annular flange 133 extending inwardly from the inner wall of the shield 130. Engaged by the studs 132 and positioned between the flange 133 and the face plate 89 are the compression springs 134 which urge the flange 133 and the supported shield 130 in a forward direction. The shield 130 extends just beyond the inner surface of the face plate 82, and has disposed along its peripheral edge a collar 135 which in turns supports in coaxial relationship with the shield 130 the shield 131, the shield 131 extending beyond the front face of the ion source 100. It should be noted that the shields 130 and 131, the face plate 89, as well as the standard 90, the yoke 94 and the ion source 100, are at substantially the same potential, whereas the cathode lead casing 125 is at a relatively small negative potential with respect to the aforementioned members which are at a high positive potential with respect to the calutron tank. Further, a cylindrical shield 136 extends from the face plate 82 and is spaced from and surrounds the cylindrical shield 131. Moreover, the inner shield 131 has projecting from its outer face oppositely disposed fins or horizontal protuberances 137 which extend longitudinally along the entire length of the inner shield 131. Further, the outer shield 136 has formed therein longitudinally extending concavities 138 cooperating with the fins or protuberances 137 which extend into the concavities 138. It should be noted that the spacing between the shields 131 and 136 and the associated protuberances 137 and concavities 138 are substantially uniform and are of such magnitude as to prevent electrical discharge therebetween at pressures .at which thecalutron is normally operated.

The accelerating structure of the calutron transmitter is mounted on the face plate 82 and comprises a pair or" arms 140 projecting from the face plate 82 and supporting at their forward ends the inwardly projecting arms 141, which in turn have mounted thereon the accelerating electrode support '142. Further, the accelerating electrode support 142 has positioned thereon the accelerating electrode 143, which has formed therein a vertical slit 144 in parallel arrangement with the are slit 110 formed in the electrode 109. Moreover, a diskshaped shield 145, having a flange 146 along its periphery, is supported by the horizontal arms 141 of the accelerating structure, and is arranged parallel to and spaced from a disk-shaped shield 147 which in turn is mounted on the front face of the ion source 100. It should be noted that the accelerating structure, the accelerating electrode 143 and the disk-shaped shield 145 are electrically connected to the face plate 82, which in turn is at ground potential, and the disk-shaped shield 147 is at the relatively high positive potential of the ion source 100.

The inner shields 130 and 131 are provided with a cooling arrangement which comprises a tubular member 150 of copper or the like, helically shaped and disposed in heat transfer relation with the inner faces of the shields 130 and 131. The ends of the tubular member 150 pass through the face plate 89 and terminate in the coupling members 151. Any liquid cooling medium such as water or oil may be circulated through the tubular member 156, whereby any heat accumulating on the inner shields 130 and 131 is conveniently removed. Further, in order to facilitate the evacuating of the region surrounded by the shields a plurality of apertures 152 are formed through the walls of the shields 130, 131 and 136 through which apertures the aforesaid region may be pumped out.

Considering now the operation of the ion source shielding arrangement described above, the transmitter is mounted on the end wall 80 of the calutron tank and the tank is then evacuated. Thereafter a vertical magnetic field is established through the calutron tank and the associated transmitter, the ion source 100 is adjusted to produce ions of the material to be separated and is raised to a high positive potential with respect to the accelerating electrode 143 whereby a ribbon-like beam of ions of high velocity is projected into the magnetic field, as has been hereinbefore described. Inasmuch as the inner shields 130, 131 and 147 and the protuberances 137 are at the high positive potential of the ion source 100 and its associated supporting structure, including the horizontal standard 90 and yoke member 94, and the outer shields 136 and 145 are at the same potential as the surrounding tank and accelerating structure, the high electric field is confined to the region between the shields. Further, the oscillating electrons are limited to a region bounded by vertical planes which are tangent to the outer edges of the protuberances 137 and by the inner surfaces of the concavities 138. Electrons occurring outside these regions and between the inner and outer shields 131 and 136 have their projections along the magnetic field intercepted by a surface at a relatively high positive potential, and such electrons terminate on the positive surface and are thus prevented from oscillating and traversing a long path, whereby additional ions and electrons are produced. Since the volume of the region of electron oscillation above defined is substantially less than the corresponding volume between a pair of similarly disposed coaxial shields without the protuberance-concavity arrangement, the results are less ionization and electron oscillation and, consequently, smaller current drain and reduced wear of the component parts of the calutron transmitter, such as the insulator bushing 84.

in the illustrated embodiment of the invention, the shielding arrangement has been disclosed as applied to the ion source unit of a calutron; however, it will be understood that this shielding arrangement is generally applicable to other parts of the calutron that are at high potentials with respect to the surrounding region and that are positioned in the magnetic field.

While there has been described what are at present considered to be preferred embodiments of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the 10 appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a calutron including a tank and means for establishing a magnetic field through said tank, a face plate associated with said tank and electrically connected thereto, an ion source mechanism mounted on said face plate and insulated therefrom, means connected to said ion source mechanism for impressing a positive potential with respect to said tank, a first electric shield disposed within said tank and surrounding said ion source mechanism, said electric shield being electrically connected to said face plate and having a concavity formed in opposing walls thereof, a second electric shield disposed between said first electric shield and said ion source mechanism and haivng a pair of opposing fins extending therefrom into said concavity, said fins being substantially normal to said magnetic field.

2. In a calutron including a tank, a face plate removably associated with said tank, an insulator carried by said face plate, an ion source carried by said insulator and arranged in said tank, a first electric shield surrounding said ion source and carried by said insulator, said first electric shield being electrically connected to said ion source, a second electric shield surrounding a portion of said first electric shield and spaced therefrom, said second electric shield being carried by said face plate and electrically connected thereto, structure mounted on said face plate and supporting an accelerating electrode adjacent the outer end of said ion source and cooperating therewith, a third electric shield arranged adjacent the outer end of said ion source and electrically connected thereto, and a fourth electric shield carried by said structure adjacent said third electric shield and electrically connected to said face plate.

3. In a calutron including a tank and having means for establishing a magnetic field therethrough, the combination comprising an ion source positioned within said tank and having impressed thereon a positive potential with respect to said tank, a first shield surrounding said ion source and having a pair of oppositely disposed fins extending outwardly normal to said magnetic field, said first shield being electrically connected to said ion source, and a second shield surrounding said first shield and having oppositely disposed concave portions to receive an end portion of said fins respectively in insulated relation thereto, said second shield being electrically connected to said tank, whereby electron oscillation is confined to the space between the ends of said fins and the interior surfaces of said concave portions.

4. In an electric device, the combination comprising an ion source, a first hollow member surrounding said ion source and electrically connected thereto, a second hollow member surrounding said first member and c0- axial therewith, means connected between said ion source and said second member for impressing a positive potential on the former with respect to the latter, means for establishing a magnetic field transversely to the aixs of said members, conductor means connected to said first member on opposing sides thereof and extending transversely of said magnetic field into recessed portions of said second member whereby said conductors intersect a portion of said magnetic field unintercepted by said second member.

5. In a calutron including a tank and having means for establishing a magnetic field therethrough, the combination comprising an ion source disposed within said tank, a first shield having a cylindrical configuration with oppositely disposed concave portions extending the length thereof, means connected between said ion source and said first shield for rendering the former positive with respect to the latter, a second shield electrically connected to said ion source and disposed between said first shield and said ion source, said second shield having a pair of oppositely disposed protruding portions extending; into said concave portions and lying in a plane transverse to said magnetic field.

6. In electrical apparatus, the combination comprising an. evacuated envelope, an electron emissive element disposed in said envelope, an electron collecting element spaced apart from said emissive element within said envelope, means for establishing electron flow between said elements, means for establishing a magnetic field through said envelope in the direction of said electron flow, a first hollow member surrounding said elements and having a pair of oppositely disposed concave portions, a second member disposed between said first memher and said elements and having a pair of oppositely disposed protruding portions extending transversely of said magnetic field into said concave portions, said second member being electrically connected to said electron collecting element, and means connected between said 12 first member and. said electron collecting element for rendering. the former negative with respect to the latter.

References Cited in the file of this patent UNITED STATES PATENTS 1,617,179 S'rnith Feb. 8, 1927 1,924,319 Hull Aug. 29, 1933 1,962,158 Smith June 12, 1934 2,039,101 McArthur Apr. 28, 1936 2,219,033 Kuhn Oct. 22, 1940 2,232,031) Kallmaimet al Feb. 18, 1941 2,245,998 Pietsch June 17, 1941 2,261,569 Schnt'ze Nov. 9, 1941 2,355,658 Lawlor' Aug. 15, 1944 2,373,151- Taylor Apr. 10, 1945 2,374,205 Hoskins Apr. 24, 1945 

1. IN A CALUTRON INCLUDING A TANK AND MEANS FOR ESTABLISHING A MAGNETIC FIELD THROUGH SAID TANK, A FACE PLATE ASSOCIATED WITH SAID TANK AND ELECTRICALLY CONNECTED THERETO, AN ION SOURCE MECHANISM MOUNTED ON SAID FACE PLATE AND INSULATED THEREFROM, MEANS CONNECTED TO SAID ION SOURCE MECHANISM FOR IMPRESSING A POSITIVE POTENTIAL WITH RESPECT TO SAID TANK, A FIRST ELECTRIC SHIELD DISPOSED WITHIN SAID TANK AND SURROUNDING SAID ION SOURCE MECHANISM, SAID ELECTRICAL SHIELD BEING ELECTRICALLY CONNECTED TO AID FACE PLATE AND HAVING A CONCAVITY FORMED IN OPPOSING WALLS THEREOF, A SECOND ELECTRIC SHIELD DISPOSED BETWEEN SAID FIRST ELECTRICAL SHIELD AND SAID ION SOURCE MECHANISM AND HAIVING A PAIR OF OPPOSING FINS EXTENDING THEREFROM INTO SAID CONCAVITY, SAID FINS BEING SUBSTANTIALLY NORMAL TO SAID MAGNETIC FIELD. 